Method of Bonding Perfluoroelastomeric Materials to a Surface

ABSTRACT

The invention includes a method of bonding a perfluoroelastomer material to first surface that includes: (a) contacting a first surface with a bonding agent comprising a curable perfluoropolymer and a curing agent; (b) curing the bonding agent to form a perfluoroelastomer material that is bonded to the first surface. In the practice of such method, the bonding agent may be a solution prepared by dissolving the curable perfluoroelastomer and the curing agent in a solvent. In an embodiment of the invention, the perfluoroelastomer material formed in step (b) is a coating layer or, alternatively, the first surface is a surface of a perfluoroelastomer member and the perfluoroelastomer material formed is a perfluoroelastomer weld.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNos. 60/897,660, filed Jan. 26, 2007 and 60/897,651, filed Jan. 26,2007, the contents of each of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

Perfluoroelastomers have readily been used to form various types ofO-rings or seals. Such seals are commonly manufactured by firstproducing a complete mold for the seal in the desired seal configurationand then compression molding a compound that includes perfluoropolymersalong with curing agents to form a completely cured perfluoroelastomerseal or other part. However, with the ever-increasing need for largerand larger seals or unusual configurations, molding complete partsbecomes more and more expensive and less of an economical practicality.This is because to form such parts requires not only the molds but alsoan infrastructure sufficient to handle the large or unusually sizedmolds, including presses and pumps related to molding operations.

One approach developed to address this need has been to produce sealsfrom rod stock and splice the two rod stock ends together to form therequired size seal. Traditional splicing techniques have not proven verysuccessful with perfluoroelastomers. Splicing with an adhesive providesa weak point in the seal that is prone to attack because adhesivesdeveloped in the past generally do not match the chemical resistance ofperfluoroelastomers.

Methods of bonding a cured perfluoroelastomer to itself using athermoplastic perfluoropolymer bonding agent have been disclosed.However, such processes result in fusing of the perfluoroelastomer endsleading to an intermediate fusing layer i.e., a layer of fusedperfluoropolymer. This provides a non-homogenous section within theperfluoroelastomer part i.e., the fused perfluoropolymer layer. Thus,the fused perfluoropolymer could result in a “weak” point due toincreased susceptibility to chemical or physical attack, increasedcompression set and reduced low temperature compliance than the rest ofthe perfluoroelastomer seal material. There is, therefore, a need in theart for an improved method of bonding and/or welding perfluoroelastomersand parts formed from them that is simple and economical and providesfor a homogenous finished part that substantially retains the strengthof a solid finished piece.

In addition to the challenges associated with joining perfluoroelastomersurfaces, it is noted that perfluoroelastomers, by virtue of the mannerin which they are typically cured and formed as noted above, and theirunique vulcanization properties (included physical and solubilityproperties) have not, however, been successfully adopted for certainuses and applications in which their chemical resistance and elastomericproperties would otherwise be advantageous, such as in surfacepassivation or other coating use.

Whereas attempts have been made to dissolve curable perfluoropolymers influorinated solvents, such as, Fluorinert® FC-40, FC-75 and FC-77 to tryto prepare coatings, the resulting coatings are typically not resistantto flow or to certain solvents, because the coatings were notcross-linked. Attempts to incorporate curatives, such as, organicperoxides with associated co-curatives; such as, triallyl isocyanurate(TAIC), were unsuccessful due to the poor solubility of suchhydrocarbon-containing curatives in the highly fluorinated solventsneeded to dissolve the uncured perfluoropolymer. Likewise,bisphenyl-based curatives, such as bisaminophenol (BOAP) typically alsoexhibit poor solubility in such highly fluorinated solvents needed todissolve perfluoropolymers curable with BOAP such as those withcyano-group containing curesite monomers.

This lack of the ability to cure high molecular weight curableperfluoropolymers in solution has restricted the use ofperfluoroelastomer coatings to non-critical applications where “flow” ofthe uncured material is acceptable.

Attempts have been made to form perfluoroelastomer coatings in the past,however, the uses and particular perfluoropolymer systems formed intocoatings are limited. U.S. Pat. No. 6,523,650 provides one example ofuse of a perfluoroelastomer coating on an electrostatic printingcomponent as an outer coating. The patent describes dissolving anelastomeric DuPont Kalrez® perfluoroelastomer, derived from3-phenoxypropylvinyl ether and at least one fluorine-containingethylenically unsaturated monomer, in solvent and applying it as acoating. However, the patent does not describe whether theperfluoroelastomer is in a cured state upon dissolution and/or how thecure system is affected by dissolution.

U.S. Pat. No. 5,268,002 teaches coating of pellicles for photomaskapplications with a coating formed of a low molecular perfluoroelastomerpolymer that acts as an antireflective coat for the pellicles. Suchpellicles have a core layer of a polymer, such as nitrocellulose, amongothers. The perfluoroelastomer polymers include tetrafluoroethylene(TFE), perfluoroalkylvinyl ether (PAVE) and a curesite monomer such asperfluoro-(8-cyano-5-methyl-3.6-dioxa-1-octene) (8-CNVE). The patentuses such polymers to form low molecular weight perfluoroelastomershaving these components by pyrolyzing the elastomer noted above and thendissolving the low molecular weight polymer in a fluorocarbon solventsuch as Fluorinert® FC-40, Fluorinert® FC-75 or Fluorinert® FC-77. Thepyrolysis enhances the solubility to enable the resulting materials tobe used in coating form. See also, U.S. Pat. No. 5,256,747.

Moreover, there is a need in the art for an easy-to-form surface coatingthat can incorporate the advantages of a standard perfluoroelastomericcoating (as opposed to a low molecular weight coating), includingallowing for use of a standard cure system and final curedperfluoroelastomer compound without complex process steps, whilemaintaining desired coating properties suitable for use on processequipment and the like and a process for preparing the same. Theinvention disclosed herein addresses this need and the need for a methodof perfluoroelastomer joining or splicing disclosed above.

BRIEF SUMMARY OF THE INVENTION

Included within the several embodiments of the invention is a method ofbonding a perfluoroelastomer material to first surface that includes:(a) contacting a first surface with a bonding agent comprising a curableperfluoropolymer and a curing agent; and (b) curing the bonding agent toform a perfluoroelastomer material that is bonded to the first surface.In the practice of such method, the bonding agent may be a solutionprepared by dissolving the curable perfluoroelastomer and the curingagent in a solvent. In an embodiment of the invention, theperfluoroelastomer material formed in step (b) is a coating layer or,alternatively, the first surface is a surface of a perfluoroelastomermember and the perfluoroelastomer material formed is aperfluoroelastomer weld.

In one embodiment of the method, the first surface is a surface of aperfluoroelastomer member, the bonding agent is also contacted to asecond surface and step (c) further includes curing the bonding agent toform a perfluoroelastomer weld between the first surface and the secondsurface. Upon curing, the perfluoroelastomer weld includes essentiallythe same perfluoroelastomer as the perfluoroelastomer member.

An embodiment of the invention also includes method of forming aperfluoroelastomer coating that includes: (a) dissolving a curableperfluoropolymer and a curing agent in a solvent to form a solution, (b)applying the solution to a surface; and (c) curing the perfluoropolymerto form a cured perfluoroelastomeric coating on the surface.Additionally, coated substrates including a cured perfluoroelastomercoating applied on at least one surface of the substrate are also withinthe scope of the invention.

In another embodiment of the invention a method of bonding aperfluoroelastomer member to a surface is disclosed. The method includes(a) contacting a first surface of a perfluoroelastomer member with abonding agent comprising: a curable perfluoropolymer, and a curingagent; (b) placing the bonding agent also in contact with a secondsurface; and (c) curing the bonding agent to form a perfluoroelastomerweld between the first and second surface, wherein upon curing theperfluoroelastomer weld comprises essentially the sameperfluoroelastomer as the perfluoroelastomer member.

In another embodiment, a method of bonding a perfluoroelastomer seal toa gland is disclosed and includes placing a bonding agent comprising acurable perfluoropolymer and curing agent within gaps formed between aperfluoroelastomer seal and a gland; and curing the bonding agent;wherein upon curing, the perfluoropolymer forms essentially the sameperfluoroelastomer as the perfluoroelastomer seal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a flowchart of a method embodiment of forming aperfluoroelastomer coating;

FIG. 2 is an enlarged perspective for cross-sectional view of aperfluoroelastomer coating made in accordance with an embodiment of thepresent invention;

FIGS. 3 a and 3 b are perspective views of a conventional rod stockmaterial;

FIG. 4 is a perspective view of an embodiment of a splicing fixture ofthe present invention;

FIG. 4 a is a partial, enlarged, exploded side elevational view of therod stock material in FIG. 3 a;

FIG. 4 b is a partial cross-sectional view of the rod stock material inFIG. 4 a taken along line 4 b-4 b in FIG. 4;

FIG. 5 is a plan view of a perfluoroelastomer seal within a gland;

FIG. 5 a is a cross-sectional view of the perfluoroelastomer seal ofFIG. 5;

FIG. 6 is a flowchart of a method of bonding a perfluoroelastomer;

FIG. 7 is a flowchart of a method of bonding a perfluoroelastomer sealto a gland; and

FIG. 8 is large perfluoroelastomer seal made in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Described herein are methods of bonding a perfluoroelastomer material tofirst surface and, optionally, a second surface. Also included arearticles, such as seals and coated substrates that are made using themethods. A perfluoroelastomer material, as used herein, may be any curedelastomeric material derived by curing a perfluoroelastomer (as definedherein) that includes a curable perfluoropolymer having a crosslinkinggroup to permit cure. A perfluoroelastomer is substantially fluorinated,and preferably completely fluorinated with respect to the carbon atomson the backbone of the perfluoropolymer. It will be understood that someresidual hydrogen may be present in perfluoroelastomers within thecrosslinks due to use of hydrogen in the functional crosslinking groupin some perfluoroelastomer formulations. In general,perfluoroelastomers, once cured are used, for example, as cross-linkedpolymeric formed articles such as seals.

The perfluoropolymers used to form perfluoroelastomer material upon cureare themselves formed by polymerizing one or more perfluorinatedmonomers, one of which is preferably a perfluorinated curesite monomerhaving a functional group to permit curing.

As used herein, a perfluoroelastomer is a polymeric composition thatincludes a curable perfluoropolymer formed by polymerizing two or moreperfluorinated monomers, including at least one perfluorinated monomerthat has at least one functional group to permit curing i.e., at leastone curesite monomer. Such perfluoroelastomer can include two or more ofvarious perfluorinated copolymers of at least one fluorine-containingethylenically unsaturated monomer, such as tetrafluoroethylene (TFE), aperfluorinated olefin, such as hexafluoropropylene (HFP), and aperfluoroalkylvinyl ether (PAVE) which includes alkyl groups that arestraight or branched and which include one or more ether linkages, suchas perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether),perfluoro(propyl vinyl ether) and similar compounds. Useful examples ofPAVEs include those described in U.S. Pat. No. 5,001,278, and in WO00/08076, of which the disclosures related to types of PAVEs are hereinincorporated by reference. Other suitable PAVEs are described, forexample, in U.S. Pat. No. 5,696,189 and 4,983,697, of which thedisclosures related to types of PAVEs are also herein incorporated byreference.

Preferred perfluoropolymers are those which meet the industry accepteddefinition of a perfluoroelastomer listed as an FFKM in ASTM D-1418-05and, are also preferably terpolymers or tetrapolymers of TFE, PAVE, andat least one perfluorinated cure site monomer which incorporates afunctional group to permit crosslinking of the terpolymer, at least oneof which is a curesite capable of being cured by the curatives describedherein.

Preferred perfluoroelastomer polymers for use in the present inventionare either commercially available as curable perfluoropolymers or areknown to be manufactured and/or sold by Daikin Industries, Inc., SolvaySolexis, Dyneon, E.I. Du Pont de Nemours, Inc., Federal State UnitaryEnterprise S. V. Lebedev Institute of Synthetic Rubber in Russia, andNippon Mektron in Japan.

In an embodiment, the invention includes perfluoroelastomer materialsthat are perfluoroelastomer coatings, and methods of manufacturing suchcoatings, and perfluoroelastomer materials that are welds acting toconnect or splice a first surface to a second surface.

Embodiments including these are formed, in part, by cure of aperfluoroelastomer by a curing agent. Preferred are peroxide-curablesystems as well as cyano-curable systems. With regard toperoxide-curable systems, preferred polymers include terpolymers of TFE,PAVEs such as those described in U.S. Pat. No. 5,001,278 (incorporatedherein in relevant part reference), and a curesite monomer having aperfluorinated structure with a peroxide-curable functional groupincluding those known or to be developed in the art, such as halogenatedalkyl and other derivatives, and partially- or fully-halogenatedhydrocarbon groups.

Regarding cyano-curable systems, most preferred are perfluoropolymers asdescribed in WO 00/08076, incorporated herein by reference or othersimilar structures. The monomers in the tetrapolymer of WO 00/08076include tetrafluoroethylene, perfluoromethylvinyl ether and two curesitemonomers, a secondary cyano curesite monomer, CF₂═CFO(CF₂)₃OCF(CF₃)CNand a primary cyano curesite monomer, CF₂═CFOCF₂CF(CF₃)O(CF₂)₂CN.Preferred compounds are those having a Mooney viscosity (measured at100° C. on a TechPro® viscTECH TPD-1585 viscometer) of about 45 to about95, and preferably of about 45 to about 65.

Primary curing agents for are peroxide-based cure systems may be anyknown peroxide curing and co-curing agents known or to be developed inthe art, such as organic and dialkyl peroxides. For the cyano-basedpolymers, preferred primary curing agents include monoamidines andmonoamidoximes as described as U.S. Patent Publication No.US-2004-0214956-A1, the disclosure of which is incorporated herein byreference in relevant part. While such monoamidines and monoamidoximesare described as potential cure accelerators or as curatives in theprior art, in the present invention they are preferably used as primarycuring agents.

The amidine-based and amidoxime-based materials include monoamidines andmonoamidoximes of the following formula (I) described further below.Preferred monoamidines and monoamidoximes may be represented by formula(I):

wherein Y may be a substituted alkyl, alkoxy, aryl, aralkyl or aralkoxygroup or an unsubstituted or substituted fully or partially halogenatedalkyl, alkoxy, aryl, aralkyl or aralkoxy group having from about 1 toabout 22 carbon atoms. Y may also be, and preferably is, aperfluoroalkyl, perfluoroalkoxy, perfluoroaryl, perfluoroaralkyl orperfluoroaralkoxy group of from 1 to about 22 carbon atoms and morepreferably a perfluoroalkyl or perfluoroalkoxy group of from about 1 toabout 12 carbon atoms, and more preferably from 1 to 9 carbon atoms; andR¹ may be hydrogen or substituted or unsubstituted lower alkyl or alkoxygroups of from one to about 6 carbon atoms, oxygen (such that NHR¹ is aNOH group) or an amino group. R² may be independently any of the groupslisted above for R1 or hydroxyl. Substituted groups for Y, R¹ or R²include, without limitation, halogenated alkyl, perhalogenated alkyl,halogenated alkoxy, perhalogenated alkoxy, thio, amine, imine, amide,imide, halogen, carboxyl, sulfonyl, hydroxyl, and the like. If R¹ and R²are both selected as oxygen and hydroxyl, such that there are two NOHgroups on the compound (a dioxime can be used), and in that case,formula (I) can be further modified to accommodate a dioxime formula inwhich the carbon atom and the Y group together form an interveningaromatic ring and in which the NOH groups are located ortho-, para- ormeta- to one another on the ring, such as with p-benzoquinonedioxime.

Preferred embodiments include those according to formula (I) in which R²is hydroxyl, hydrogen or substituted or unsubstituted alkyl or alkoxygroups of from 1 to 6 carbon atoms, more preferably hydroxyl orhydrogen. Also preferred are embodiments in which R¹ is hydrogen,oxygen, amino or a substituted or unsubstituted lower alkyl of from 1 to6 carbon atoms while R² is hydrogen or hydroxyl. Most preferred areembodiments where R¹ and R² are both hydrogen. Further preferredembodiments include those in which Y is perfluoroalkyl, perfluoroalkoxy,substituted or unsubstituted aryl groups and substituted orunsubstituted halogenated aryl groups having the chain lengths as notedabove, particularly preferred are when R¹ and R² are both hydrogen and Yis CF₃(CF₂)₂— (i.e., when the compound is heptafluorobutyrlamidine) or asimilar amidoxime compound.

Exemplary monoamidine-based and monoamidoxime-based curatives accordingto formula (I) include perfluoroalkylamidines, arylamidines,perfluoroalkylamidoximes, arylamidoximes and perfluoroalkylamidrazones.Specific examples include perfluorooctanamidine,heptafluorobutyrylamidine, benzamidine, trifluoromethylbenzamidoxime,and trifluoromethoxybenzamidoxime, with heptafluorobutyrlamidine beingmost preferred. Curatives as noted according to formula (I) may be usedalone or in combinations, such as in combinations of preferred and/orexemplary compounds noted hereinabove or with secondary curatives.

The curatives according to formula (I) are preferably capable of curingperfluoroelastomeric compositions, particularly those with at least onecyano curesite monomer.

Other curative (curing agents) may include perfluoroelastomerformulations can include bisphenols and their derivatives,tetraphenyltin, triazine, peroxide-based curing systems (e.g., organicperoxides such as dialkyl peroxides), or combinations thereof. Othersuitable curing agents include oganometallic compounds and thehydroxides thereof, especially organotin compounds, including ally-,propargyl-, triphenyl- and allenyl tin, curing agents containing aminogroups such as diamines and diamine carbamates, such asN,N′-dicinnamylidene-1,6-hexanediamine, trimethylenediamine,cinnamylidene trimethylenediamine, cinnamylidene ethylenediamine, andcinnamylidene hexamethylenediamine, hexamethylenediamine carbamate,bis(4-aminocyclohexly)methane carbamate, 1,3-diaminopropanemonocarbamate, ethylenediamine carbamate, trimethylenediamine carbamate,bisaminothiophenols, bisamidoximes, and bisamidrazones. Most preferablya peroxide cure system (including any necessary co-agents) is used.

The curing system does not require, but may also optionally include avariety of secondary curatives, such as bisphenyl-based curatives andtheir derivatives, tetraphenyltin, triazine, peroxide-based curingsystems (e.g., organic peroxides such as dialkyl peroxides) (if not usedas a primary agent or if used in a combination of peroxides, orcombinations of these systems. Other suitable secondary curing agentsinclude oganometallic compounds and the hydroxides thereof, especiallyorganotin compounds, including ally-, propargyl-, triphenyl- and allenyltin, curing agents containing amino groups such as diamines and diaminecarbamates, such as N,N′-dicinnamylidene-1,6-hexanediamine,trimethylenediamine, cinnamylidene trimethylenediamine, cinnamylideneethylenediamine, and cinnamylidene hexamethylenediamine,hexamethylenediamine carbamate, bis(4-aminocyclohexly)methane carbamate,1,3-diaminopropane monocarbamate, ethylenediamine carbamate,trimethylenediamine carbamate, and bisaminothiophenols.

Other optional additives for use with the various perfluoroelastomerformulations can include the addition of fillers such as graphite,carbon black, clay, silicon dioxide, polymeric graphite, fluoropolymericparticulates (e.g., TFE homopolymer and copolymer micropowders), bariumsulfate, silica, titanium dioxide, acid acceptors, cure accelerators,glass fibers, or polyaramid fiber such as Kevlar®, plasticizers, orother additives known or to be developed in the perfluoroelastomericart. However, it is preferred for coating compositions used insemiconductor and other particulate-sensitive applications, that suchoptional fillers not be used, or that clean fillers (silica, bariumsulfate or fluoropolymer particulates) be used.

The bonding agent, which bonds to the first and/or to the second surface(particularly for forming a weld-type connection), includes a curableperfluoropolymer and a curing agent. The components of the bonding agentmay be individually dissolved and then combined followed by an in situcuring cycle. However, it is also within the scope of the invention tofirst compound the components and then dissolve the compound in asolvent. Methods of compounding bonding agent components may beaccording to any known technique in the art or any to be developed and adetailed explanation of the compounding and processing methods are notnecessary for a complete understanding of the present invention. Forexample, conventional methods of compounding are described inInternational Plastics Handbook, 3^(rd) Edition, Saechtling, p. 54-55.However, it is preferred that the primary individual components are eachfirst dissolved in a solvent(s) prior to combination.

In dissolving the components or formulation, the preferred solvent fordissolution of the curable perfluoropolymer is a fluorosolvent that isable to dissolve at least the curable perfluoropolymer component, andmore preferably, that is able to also dissolve the curative(s). Solventshaving the desired characteristics are known in the art and includeFluorinert® FC-87, FC-84, FC-75, FC-77 and/or FC-43, commerciallyavailable from 3M and any similar solvents. However, it should beunderstood that while such fluorinated solvents are preferred, anysolvent which is known or to be developed, that is capable of dissolvingthe compounded curable perfluoropolymer, and preferably the curativeand/or the primary components in the compounded perfluoroelastomerformulation (i.e., the perfluoropolymer and the curative aside from anyadditives) may be used within the scope of this invention.

Preferably the total amount of solvent to be used is about 70% to about95% by weight, more preferably about 90% to about 95% by weight, andmost preferably about 94% to about 95% by weight of the finishedsolution prior to cure.

The curable perfluoropolymer is preferably present in a finishedsolution in an amount about 1% to about 25% by weight, more preferablyabout 1% to about 10% by weight, and most preferably about 1% to about5% by weight, based on the total weight of the finished solution. Thecuring agent is preferably present in an amount of about 0.01% to about5%, more preferably about 0.01% to about 1.5%, and most preferably about0.25% to about 1% based upon total weight of the finished solution priorto cure. It is preferred that the weight percentage ratio ofperfluoropolymer to curing in the finished solution be about 30:1 toabout 10:1, and more preferably about 20:1.

In making the finished solution, the bonding agent may be initiallycompounded to form a compounded bonding agent and then dissolved insolvent in accordance with the above preferred percentages. In such amethod, the compounded fluoropolymer might first be formed into smallpieces by, for example, a clicker die, although any other die cutter,knife, scissor, or similar cutting apparatus suitable for the intendeduse can be used. Preferably the pieces range from about 0.010 inches toabout 0.250 inches in size and more preferably about 0.030 inches onaverage. The pieces can optionally be ground into finer sized pieces.Preferably, the pieces are then added to a solvent, such as thosementioned above, and then mixed. Mixing the pieces in the presence of asolvent, for example on a ball mill, facilitates the dissolution of theperfluoropolymer formulation into the solvent.

More preferably, each of the primary components of the bonding agent isfirst dissolved in solvent. In such a method, a first solution (solutionA) is formed by combining the curable perfluoropolymer with a solvent inan amount of about 2 to about 50% by weight curable perfluoropolymer,more preferably 2 to 20% by weight and most preferably 5 to 10% byweight based on the total weight of the first solution. A separatesolution (solution B) is formed by combining the cure agents with asolvent in an amount of about 0.02% to about 10%, more preferably about0.02% to about 3%, and most preferably about 0.50% to about 2% based onthe total weight of the second solution. Then the two solutions aresubsequently combined by taking equal parts of each solution andcombining them to achieve the desired percentage of the curableperfluoropolymer and curative(s) in the finished solution. If additivesare used, they may be added in either of the two initial solutions or inthe finished solution in accordance with this particular method.

In an embodiment where the bonding agent is applied to the surface of aperfluoroelastomer member, the bonding agent of the present embodimentis made using the same or substantially the same perfluoroelastomerformulation as used to produce the rod stock to which it is to bewelded. In the present embodiment, the bonding agent can include any ofthe compounded perfluoroelastomer formulations as described above, whichinclude a curative(s).

In an embodiment, the invention includes a method of bonding aperfluoroelastomer material to a first surface by contacting a firstsurface with a bonding agent comprising a curable perfluoropolymer and acuring agent and curing the agent to form a perfluoroelastomer materialthat is bonded to the first surface such that the perfluoroelastomermaterial formed is a coating layer. In such embodiments, the bondingagent may be a solution that can be applied to a surface of a substrateby any number of conventional means such as spray coating, dip coating,brushing, layering, and the like. With reference to FIG. 2, a coatedsubstrate, generally referred to as 10, is formed by applying thefinished solution to an uncoated substrate 12. Once the bonding agentsolution is applied, it is cured in situ to form a coating 14. Once thesubstrate is coated a heat cycle is applied. The heat cycle will varydepending upon the specific perfluoroelastomer formulation used for thecuring agent, however the heat cycle can be configured to provide asufficient amount of heat for a sufficient amount of time to effectivelycure the bonding agent. Alternative curing can be used includingultraviolet, infrared or other radiative curing methods as well asoptional use of pressure. While the invention should not be restrictedto any specific cure or cure cycle, it is preferred that heat is used atabout 149° C. (300° F.) for about eight minutes. However, the curingtemperature will vary depending upon the type of perfluoropolymer andcuring agent used in the perfluoroelastomer formulation. Such curingtemperatures can range from about 138° C. (280° F.) to about 177° C.(350° F.), and preferably about 149° C. (300° F.) to about 177° C. (350°F.). One of ordinary skill in the art will understand that curingconditions vary with elastomer systems and that such temperature rangesare not intended to be limiting with respect to the scope of theinvention, since a variety of perfluoroelastomer formulations can beused.

After heat curing, post curing may optionally, but not necessarily beapplied at about 180° C. (356° F.) or other suitable post-curetemperature for about seven to eight hours or other suitable cure cycletimes, depending on the resulting properties desired. An additional cooldown time of one hour can then optionally be applied.

Although the present embodiment has been described for coating a singlesubstrate, the process may also be used to bond two substrates togetheras an adhesive or bonded layer formed in situ between two opposingsurfaces (not shown) such as in a laminated or other multi-layeredstructure. It may also be used to bond on three-dimensional, non-planarsurfaces.

The application of the present embodiment is not limited to anyparticular substrate surface type, but instead can be used to form aperfluoroelastomer coating on any type of solid surface. Suchperfluoroelastomer coatings can be used to coat foamed materials,metals, metal alloys, glass, elastomers, plastics, composites and thelike. As a result of the uniquely elastomeric and inert character ofsuch coatings, they have application in a wide variety of areas,including, semiconductor processing parts, doors, and equipment; surfacepassivation; handling or mechanical tools; medical equipment anddevices; automotive and aerospace parts and surfaces, equipment subjectto high corrosion (e.g., oil field and catalytic process equipment) andthe like. In addition, the coatings as formed are highly chemicallyinert and insoluble.

The coatings may also be used to affect a seal in applications in whichthe features are too small for conventional molded seal parts, such asin “lab-on-a-chip” applications in which a very thin silica or plasticlayer must be sealed with a heat- and chemically-resistant material. Thematerial coatings may also be used as sealants on metal surfaces such asthose in aircraft engine parts where in-service use conditions exceedthe temperature range for other elastomers such as nitriles or standardfluoroelastomers (such as Viton®).

When pressures or temperatures exceed the capabilities of typicalelastomer seals, there are current uses involving metal-to-metal seals.However, these seals must be highly polished to affect a seal. Itsubstantially increases the cost of forming such seals. However,application of a thin coating as described herein on such a substratecan affect a seal between metal parts using a less polished and lessexpensive metal surface.

Such solutions and cured coatings can also be used to repair or adhereto surfaces of expensive perfluoroelastomer molded parts (such asO-rings, seals, gaskets and the like).

In an embodiment, the present invention provides for a method (asillustrated in FIG. 6) of bonding perfluoroelastomer (“FFKM”) members,for example to form a seal (e.g., an O-ring or similar shaped seal) outof rod stock. The term “rod stock” as used herein means any preformedstock material, regardless of shape or cross-sectional configurationthat can be used to make a seal.

The rod stock 11, 20 (FIGS. 3 a and 3 b) is pre-formed using anyconventional molding process such as extrusion or compression molding.Such molding processes are well known in the art and a detailedexplanation of them is not necessary for a complete understanding of thepresent invention. During the pre-form process, which is typicallyextrusion, some heat applied to the mold at least partially cures thecompounded perfluoroelastomer formulation transforming theperfluoropolymer into at least partially cured perfluoroelastomer. Theremaining curing typically occurs during post pre-form processes, suchas press-molding or oven post-cure.

With reference to FIGS. 3 a and 3 b, the perfluoroelastomer pre-form orrod stock 11, 20 (as illustrated in FIGS. 3 a and 3 b) is initiallyformed from a compounded perfluoroelastomer formulation. Preferably theperfluoroelastomer rod stock 11, 20 is at least about 25% to about 95%cured. Methods of compounding perfluoroelastomer formulations may beaccording to any known technique in the art or any to be developed and adetailed explanation of the compounding and processing methods are notnecessary for a complete understanding of the present invention. Forexample, conventional methods of compounding are described inInternational Plastics Handbook, 3^(rd) Edition, Saechtling, p. 54-55,the contents of which are incorporated herein.

The rod stock 11 has a first end 13 a with a preferred cross-sectionalsurface 15 in a shape which is generally circular. The cross-sectionalshape can alternatively be any other shape consistent with the intendeduse such as an oval, square, rectangle, or the like. The rod stock 11also has a second end 13 b with a cross-sectional surface 15 with agenerally circular shape.

As used herein, the term “weld” is meant to broadly encompass anyjoining together of two surfaces through use of a bonding agenttherebetween, whether in liquid or solid “plug” form, physically andpreferably using curable chemical crosslinking and/or bonding betweeneach of the two opposing surfaces to be welded and the bonding agent,however, it should be understood that the two opposing surfaces need notbe formed of the same material. The first end 13 a of the rod stock 11can be welded to the second end 13 b of rod stock 11 to form a circularring. Alternatively, the first end 13 a can be welded to a second rodstock 20 having ends 22 a, 22 b (as shown in FIG. 3 a) which can beformed from the same perfluoroelastomer formulation as rod stock 11. Theweld for joining various ends of perfluoroelastomer rod stock is formedby coating or applying at least one end of the rod stock with a bondingagent.

The bonding agent, either in the form of an extruded preform of theperfluoroelastomer formulation to form a solid “plug” or in the form ofa solution of the compounded perfluoroelastomer formulation is employed.As a solution, it is applied to the surface of the rod stock 11. Thebonding agent is then contacted with at least one of the surfaces to bewelded. It can be applied in liquid form as a coating to a singlesurface such as 13 a, or both opposing surfaces, such as 13 a, 13 b or22 a, 22 b, that are to be welded together. As a solid “plug,” it can bemerely inserted between two surfaces to be welded in a manner such thatthe plug will contact the surfaces upon later curing and processing. Asa plug, the preform is situated next to, for example, a rod stock 11surface, preferably contacting the surface.

In operation, when using a bonding agent in solution to weld two ends ofperfluoroelastomer rod stock together, for example to form an O-ring, atleast one surface of one of the ends e.g., 13 a is initially coated withthe bonding agent. The coating can be applied by any number ofconventional means such as spray coating, dip coating, brushing,layering, and the like. The second end 13 b of the rod stock 11 may alsooptionally be coated with the bonding agent when welding two ends of thesame rod stock. The two ends of the coated rod stock 13 are then placedin a fixture 30 (e.g., a splicing fixture as shown in FIG. 4) to secureone end 13 a adjacent to or in contact with the second end 13 b of therod stock 10 (as shown in FIG. 4 a). The fixture 30 can be configured toaccommodate the rod stock 11 for size and alignment and to allow heatand pressure to be exerted on the rod stock 11 to hold them in placewithin the fixture 30. The heat and pressure are generally supplied by apress, in which the fixture is mounted and operated. The fixture 30 canoptionally act to apply a heat cure cycle to the bonding agent.

The fixture 30 includes a bottom portion 32 and a top portion 34. Thetop 34 and bottom 32 portions include channels 36 a, 36 b respectivelyfor seating the rod stock material. A hinge 38 connects the top 34 andbottom 32 portions to allow the fixture 30 to open and close and toalign the top and bottom portions of the channel 36 a, 36 b.

After placing the coated rod stock 10 in the fixture 30, the fixture 30is closed and a heat cycle is applied. The heat cycle will varydepending upon the specific perfluoroelastomer formulation used for thecuring agent, however the heat cycle can be configured to provide asufficient amount of heat for a sufficient amount of time to effectivelycure the bonding agent. An effectively cured bonding agent is one thatresults in at least a partially cured perfluoroelastomer (preferably onewhich is cured greater than about 75%). The bonding agent is typicallycured about 75% to about 95%, or up to about 99%. In the presentembodiment, the heat cycle includes heat of about 300° F. for about 8minutes. However, the curing temperature of the heat cycle will varydepending upon the type of perfluoropolymer and curing agent used in theperfluoroelastomer formulation and employ temperatures are detailedabove in the coatings context. One of ordinary skill in the art willunderstand that curing conditions vary with elastomer systems and thatsuch temperature ranges are not intended to be limiting with respect tothe scope of the invention, since a variety of perfluoroelastomerformulations can be used.

This heat cycle contributes to substantially if not fully completing thecure reaction of the perfluoropolymer and curing agent(s) within thebonding agent that subsequently results in the same or substantially thesame perfluoroelastomer as the perfluoroelastomer of the rod stock.After the heat cycle, the spliced ends can be post cured at about 180°C. (356° F.) or other suitable post-cure temperature for about seven toeight hours or other suitable cure cycle times. An additional cool downtime of one hour can then optionally be applied. Preferably the bondingagent forming the perfluoroelastomer splice is cured to about 95% asnoted above. In addition to heat cure cycles, it is also within thescope of the invention to use infrared, UV, or other radiative curingtechniques.

This welding process can be applied to a variety of rods having multipleends to form a variety of sealing rings of varying sizes, shapes, andconfigurations. The resulting seals, which can be very large in size,have a cured, indistinguishable, and homogenous weld(s) compared toseals wholly formed from a single-step mold operation. That is, theperfluoroelastomer weld has the same or substantially the same chemicalcomposition as the perfluoroelastomer rod stock. This advantageouslyresults in the seal having the same highly resistant chemicalcomposition throughout. Thus, there are no weak points or welded endsthat are more vulnerable to chemical and/or physical attack than the rodstock bulk seal material.

Although the present embodiment has been described for bonding twosurfaces of the same rod stock or two different pieces of rod stock madefrom the same perfluoroelastomer, the present invention is not limitedto bonding such materials only. The present invention can also be usedto weld two different pieces of rod stock made from differentperfluoroelastomers, such as any of the perfluoroelastomers describedabove. Further, the invention can be used to bond or weld various othertypes of perfluoroelastomers surfaces not in rod form—in sheet form,molded form, lamination form and various other shapes.

In another embodiment, the present invention provides for a method ofpotting a perfluoroelastomer seal 40 as illustrated in FIGS. 5 and 7using a bonding agent as described in any of the above embodiments. Asused herein and shown in FIG. 5 a, the term “potting” means filling inof gaps 42 or spaces between a seal 40 and a seal gland 44. The sealgland 44 is typically formed from materials that are highly resistant tochemical attack such as aluminum and stainless steel. In thisembodiment, the bonding agent is placed within the gaps 42 between theseal 40 and the seal gland 44. After potting the bonding agent, theentire construct i.e., the seal 40, seal gland 44, and potted bondingagent, is heated to about 149° C. (300° F.) for about eight minutes. Theheat cures the bonding agent and as a result forms a perfluoroelastomerbond between the seal 40 and the seal gland 44. An advantage of thepresent embodiment is that the perfluoroelastomer seal 40 then issecurely bonded to the seal gland 44 which advantageously lowersparticulation or degradation of the primary sealing material due to theadditional perfluoroelastomer from the weld and because there is thenminimized gapping between the seal 40 and the gland through whichparticulation may migrate. In addition, the bond eliminates the relativemotion and hence abrasion, between the seal and gland, furthercontributing to lower particulation.

The application of the present embodiment is not limited to potting suchas seal against a gland having any particular composition, but insteadcan be used to pot a perfluoroelastomer seal on a variety of glandsurfaces, for example, formed of metals, metal alloys, plastics,composites and the like. However, metallic and metallic alloy surfacesare most typically encountered in such applications of use. Such pottinguses can be used in various bonded gland applications, including,semiconductor doors, gates, and other pre-bonded surface sealingapplications, and are particularly useful when such applications aresubject to high corrosion such as semiconductor manufacturingconditions.

EXAMPLE 1

In this example, a large perfluoroelastomer seal was made using Chemraz®molded subsections which had been cured, but not post-cured. One sectionwas rectangular in configuration, wherein the rectangle had roundedcorners. Two other circular sections were prepared. The rectangularsection was sliced transversely across the long-sided portions of therectangle. After cutting, two half-rectangular end pieces were formed.The circular sections were then sliced so as to form a rod, andshortened to the appropriate length to form two straight sections ofdesired length. The resultant two rectangular end pieces were joined tothe two straight sections using a bonding agent and a splicing fixtureto form a resultant part having the shape shown in FIG. 8.

The bonding agent used was prepared by first compounding aperfluoroelastomer formulation having the following constituents, asnoted in parts by weight:

Components Parts by Weight Curable Perfluoropolymer 100 Silica 9Peroxide-Based Curing Agent 1.5 Peroxide-Based Cure System 4 Co-AgentBarium Sulfate 32

After compounding, the compounded formulation was cut into small pieces,approximately 0.25 inches in size in the largest dimension using a diecutter. The pieces were then added to a jar having Fluorinert® FC-77solvent. The solvent was added so as to make-up 94% by weight of thetotal solution. The jar was then placed on a jar mill and continuouslyrolled for about forty-eight hours to form the bonding agent.

The bonding agent was coated on one end of a first rod stock member andplaced within a sealing fixture such as that shown in FIG. 4, to bewelded to a second rod stock member. The second rod stock member wasalso coated and placed so that its end was pressed against the coatedend of the first rod stock member. The sealing fixture was then closedand heated to about 149° C. (300° F.) for about eight minutes to curethe bonding agent. This welding process was performed four times at eachdesired weld to form the finished part and to create the welds to form alarge-formed seal. The overall rectangular dimensions of the finishedpart as shown in FIG. 8 were approximately 2.1 meters long×0.17 m widewith a transverse cross-sectional diameter (being generally circular intransverse configuration) of about 0.6 cm (the shape formed at the weldwas not perfectly round, but was very close). The part was thenpost-cured at 180° C. (356° F.) for 7.25 hours followed by a one hourcool down period.

EXAMPLE 2

A perfluoroelastomer coating was made by forming a first solution(Solution A). Solution A was formed by dissolving 100 parts by weight ofa curable cyano-curable perfluoropolymer prepared in accordance with WO00/08076 (a perfluoroelastomer gum having a primary and secondary cyanocuresite) in 900 parts by weight of Fluorinert® FC-43 fluid solvent from3M. A second solution (Solution B) was made by dissolving 5 parts byweight of heptafluorobutyrlamidine as a curing agent in 995 parts byweight of the same solvent used to form Solution A. Solutions A and Bwere then combined in equal parts by weight to form a finished coatingsolution. The finished coating solution was applied on a metallicsubstrate surface and subjected to a heat curing cycle of 100° C. (212°F.) for about four hours. The resulting cured perfluoroelastomer coatingwas clear. Similar coatings were also prepared on glass, plastic andsynthetic rubber.

1. A method of bonding a perfluoroelastomer material to first surfacecomprising: (a) contacting a first surface with a bonding agentcomprising a curable perfluoropolymer and a curing agent; and (b) curingthe bonding agent to form a perfluoroelastomer material that is bondedto the first surface.
 2. The method of claim 1, wherein the bondingagent is a solution prepared by dissolving the curableperfluoroelastomer and the curing agent in a solvent.
 3. The method ofclaim 2, wherein the solvent is a fluorinated solvent.
 4. The method ofclaim 2, wherein the perfluoroelastomer material formed in step (b) is acoating layer.
 5. The method of claim 2 wherein the bonding agent isprepared by a method comprising: (i) forming a first solution of thecurable perfluoropolymer and a first solvent; (ii) forming a secondsolution of the curing agent and a second solvent; and (iii) combiningthe first solution and the second solution.
 6. The method of claim 5,wherein the first solvent and the second solvent are identical.
 7. Themethod of claim 1, wherein the curing step (b) further comprises heatingfor a time period sufficient to effectively cure the perfluoroelastomermaterial.
 8. The method of claim 1, wherein the curing step furthercomprises heating to about 149° C. (300° F.).
 9. The method of claim 1,wherein step (a) comprises spraying the bonding agent onto the surface.10. The method of claim 1, wherein the curable perfluoropolymer has atleast one curesite monomer comprising a cyano group.
 11. The methodaccording to claim 1, wherein the curing agent is selected from thegroup consisting of a monoamidine, a monoamidoxime, an aryldioxime,perfluorooctamidine, heptafluorobutyrlamidine, a bisphenol or aderivative thereof, a tetraphenyltin, a triazine, and a peroxide-basedcuring system.
 12. The method of claim 1, wherein the first surface is asurface of a perfluoroelastomer member and the perfluoroelastomer formedis a perfluoroelastomer weld.
 13. The method of claim 12, wherein step(a) further comprises contacting the bonding agent to a second surfaceand step (c) further comprises curing the bonding agent to form aperfluoroelastomer weld between the first surface and the secondsurface, wherein upon curing the perfluoroelastomer weld comprisesessentially the same perfluoroelastomer as the perfluoroelastomermember.
 14. The method of claim 13, further comprising post-curing theperfluoroelastomer weld.
 15. The method of claim 14, wherein theperfluoroelastomer weld is about 95% cured.
 16. The method of claim 14,wherein the perfluoroelastomer member and the weld form a part and themethod further comprises post-curing the part.
 17. The method of claim13, wherein the bonding agent is produced by the steps comprising:compounding a perfluoroelastomer formulation to form a compound; anddissolving the compound in a solvent to form a solution, wherein thebonding agent is contacted with the first surface by coating the firstsurface with the bonding agent.
 18. A method of forming aperfluoroelastomer coating comprising (a) dissolving a curableperfluoropolymer and a curing agent in a solvent to form a solution, (b)applying the solution to a surface; and (c) curing the perfluoropolymerto form a cured perfluoroelastomeric coating on the surface.
 19. Themethod according to claim 18, wherein step (c) comprises heating thecoating layer for a sufficient period of time to effectively cure theperfluoropolymer.
 20. The method according to claim 18, wherein thecuring step further comprises heating the coating layer to about 149° C.(300° F.).
 21. The method according to claim 18, wherein step (a)further comprises (i) forming a first solution of the curableperfluoropolymer and a first solvent; (ii) forming a second solution ofthe curing agent and a second solvent; and (iii) combining the firstsolution and the second solution.
 22. The method according to claim 21,wherein the first solvent and the second solvent are identical.
 23. Themethod according to claim 18, wherein step (b) comprises spraying thesolution onto the surface.
 24. The method according to claim 18, whereinthe curable perfluoropolymer has at least one curesite monomercomprising a cyano group.
 25. The method according to claim 18, whereinthe curing agent is selected from the group consisting of a monoamidine,a monoamidoxime and an aryldioxime.
 26. The method according to claim25, wherein the curing agent is perfluorooctanaidine orheptafluorobutyrlamidine.
 27. The method according to claim 18, whereinthe solution comprises about 1% to about 25% by weight of theperfluoropolymer based on the total weight of the solution.
 28. Themethod according to claim 27, wherein the solution comprises about 1% toabout 10% by weight of the perfluoropolymer based on the total weight ofthe solution.
 29. The method according to claim 28, wherein the solutioncomprises about 1% to about 5% by weight of the perfluoropolymer basedon the total weight of the solution.
 30. The method according to claim29, wherein the solution comprises about 0.01% to about 5% by weight ofthe curing agent, based on the total weight of the solution.
 31. Themethod according to claim 30, wherein the solution comprises about 0.01%to about 1.5% by weight of the curing agent based on the total weight ofthe solution.
 32. The method according to claim 31, wherein the solutioncomprises about 0.25% to about 1% by weight of the curing agent basedupon total weight of the solution.
 33. A coated substrate comprising acured perfluoroelastomer coating applied on at least one surface of thesubstrate.
 34. The coated substrate according to claim 33, wherein theperfluoroelastomer coating is formed by a curing reaction of a curableperfluoropolymer and a curing agent in a solution applied to the surfaceof the substrate.
 35. The coated substrate according to claim 34,wherein the curable perfluoropolymer has at least one curesite monomerhaving a cyano group and the curing agent is a monoamidine,monoamidoxime or aryldioxime.
 36. The coated substrate according toclaim 35, wherein the curing agent is perfluorooctanamidine orheptafluorobutyrlamidine.
 37. A method of bonding a perfluoroelastomermember to a surface, comprising: (a) contacting a first surface of aperfluoroelastomer member with a bonding agent comprising: a curableperfluoropolymer, and a curing agent; (b) placing the bonding agent alsoin contact with a second surface; and (c) curing the bonding agent toform a perfluoroelastomer weld between the first and second surface,wherein upon curing the perfluoroelastomer weld comprises essentiallythe same perfluoroelastomer as the perfluoroelastomer member.
 38. Themethod of claim 37, further comprising post-curing theperfluoroelastomer weld.
 39. The method of claim 38, wherein theperfluoroelastomer weld is about 95% cured.
 40. The method of claim 38,wherein the perfluoroelastomer member and the weld form a part and themethod further comprises post-curing the part.
 41. The method of claim40, wherein the part is a seal.
 42. The method of claim 40, wherein thepart is homogeneous.
 43. The method of claim 38, wherein theperfluoroelastomer weld is homogeneous with the perfluoroelastomermember.
 44. The method of claim 38, wherein the first and secondsurfaces are on the same perfluoroelastomer member.
 45. The method ofclaim 38, wherein in step (a) the perfluoroelastomer member is about 75%to about 95% cured.
 46. The method of claim 37, wherein step (b) furthercomprises: placing the first surface and the second surface within afixture; and positioning the first surface, the bonding agent and thesecond surface within the fixture, such that the first surface, thebonding agent and the second surface are in contact.
 47. The method ofclaim 37, wherein step (c) further comprises heating the bonding agentfor a sufficient period of time to effectively cure the bonding agent.48. The method of claim 37, wherein step (c) further comprises heatingthe perfluoroelastomer bonding agent to about 149° C. (300° F.).
 49. Themethod of claim 37, wherein the bonding agent further comprises asolvent and the bonding agent is contacted with the first surface bycoating the first surface with the bonding agent.
 50. The method ofclaim 49, wherein the solvent is a fluorinated solvent.
 51. The methodof claim 37, wherein the curing agent is at least one of a bisphenol ora derivative thereof, a tetraphenyltin, a triazine, and a peroxide-basedcuring system.
 52. The method of claim 37, wherein the bonding agent isproduced by the steps comprising: compounding a perfluoroelastomerformulation to form a compound; and dissolving the compound in a solventto form a solution, wherein the bonding agent is contacted with thefirst surface by coating the first surface with the bonding agent andthe bonding agent is contacted with the first surface by coating thefirst surface with the bonding agent.
 53. The method of claim 52,wherein the step of dissolving comprises: forming the compound intopieces; adding about 70% to about 95% by weight solvent to the pieces ofthe compound, and dispersing the particulates of the pieces whiledissolving the pieces on a ball mill.
 54. The method of claim 52,wherein the solvent is added in an amount of about 90% to about 95% byweight of the solution.
 55. A method of bonding a perfluoroelastomerseal to a gland, comprising: placing a bonding agent comprising acurable perfluoropolymer and curing agent within gaps formed between aperfluoroelastomer seal and a gland; and curing the bonding agent;wherein upon curing, the perfluoropolymer forms essentially the sameperfluoroelastomer as the perfluoroelastomer seal.